The present invention relates to a hydraulic control system for a transmission, and more particularly to a hydraulic control system for a hybrid transmission combining a gearing mechanism with a V-belt type continuously variable transmission.
The transmissions of the above kind are known and disclosed in Japanese patent application preliminary publication Nos. 57-191134, 56-97661, and 58-146756.
An object of the present invention is to provide an improved hydraulic control system wherein any slip of a V-belt of a V-belt type continuously variable transmission mechanism is prevented even when the V-belt is subjected to the torque variation upon shifting from the torque transmission through the gearing mechanism to the torque transmission through the V-belt type continuously variable transmission mechanism.
A specific object of the present invention is to provide a hydraulic control system wherein the level of the line pressure is kept at a sufficiently high level during the torque transmission through the V-belt type continuously variable transmission mechanism without increasing the level of the line pressure beyond the necessary level for the torque transmission through the gearing mechanism.